Stabilization circuit for arc lamps



Aug. 4, 1964 L. F. BIRD STABILIZATICN CIRCUIT Foa ARC LAMPS Filed April28, 1959 M v. w B w n e e ,k my ,Wm wx. X d. m C `f a il. fr mm M l. Lma ll/l m.

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United States Patent O This invention relates to a stabilization circuitfor arc lamps and, more particularly, for high pressure arc lamps of thecompact type. *A y It has been found from life tests on high'pressurearc lamps of the compact type `that unnecessary instantaneous currentdemands from the electrodes considerably shorten the life of such lamps.Accordingly, circuits which maintain lamp voltages at the lowest valuedespite variations in line voltage yield the best useful life for thelamp. With the usual ballast for the arc composed of a .constant seriesreactance, there is no compensation for varyingrsupply voltages and thelife of the lamp is relatively short. Such arrangements also have theobvious drawback that light from the lamp will flicker with supplyvoltage variations.

It is further noted that prior circuits which have been effective foraccomplishing this purpose have generally been unnecessarily expensivein the provision of. heavy dutyregulator circuits having anVunnecessarily broad range of regulation.

Y Therefore, it is the principal objectof this invention to provide animproved operating circuit for arc lamps, in which the power supplied tothe lamp is maintained substantially constant. As a result, the usefullife of the lamp is greatly increased. As a further advantage, the lightoutput remains independent of variations in the supply voltage.

In accordance with an illustrative embodiment of the invention,stabilization for arc lamps is obtained by the use of an inductiveballast of which the impedance is regulated automatically as a functionofthe supply voltage. This is accomplished by means of a pair ofsaturable reactors, the power winding of each reactor being connected toreceive one half-wave of the supply current. In order to vary theimpedance of these power windings, two magnetic fields are applied tothe magnetic core of each-reactor. The first magnetic field has aVconstant magnetic force above that required for the impedancce at whichoptimum supply current conditions prevail. The magnetic force of thesecond field is weaker and a function of the supply voltage; it isapplied to Vthe core in opposite polarity with respect to the firstfield. By superposition both fields act combined upon the core toautomatically adjust the impedance, and therefore maintain the voltageat the arc lamp at a substantially constant value.

In practice, each reactorcore carries two control windings of which therst receives a constant direct currentY signal while the second controlwinding is energized by a direct current signal which is a function, ofthe supply voltage. Since control windings of saturable reactors mustnecessarily be energized by direct current, two reactors are required,whereby the power Winding of each reactor is associated with arectifier. Each winding receives one of the half-waves of the supplycurrent or a portion thereof as this is the case when an additional,constant impedance is connected in parallel with respect to the powerwindings.

In accordance with a feature of the invention, the heavy duty inductiveballast of an arc lamp is shunted by a magnetic amplifier having a powercapacity which is a fraction of that of the ballast. In addition,control signals which are the resultant of a constant signal combined inopposition with a variable line voltage signal are applied to change theimpedance of the shunt magnetic amplifier. e

The foregoing arrangements have the advantage of providing regulationfor an arc lamp by the addition of an inexpensive light duty magneticamplifier in parallel with the main ballast of the arc lamp circuit.Furthermore, excellent regulation is provided without changing thedesired inductive character of the series ballasting circuit for the arclamp.

In accordance with another feature ofthe invention the ballast for anarc lamp includes two saturable magnetic cores, and circuitry forapplying two magnetic fields to each core. The first field has aconstantmagnetic forcey higher than that required for optimum current supply tothe lamp. The second, weaker magnetic'fieldfvaries with the supplyvoltage and is applied to thecores in opposite polarity with respect tothe first fieldto increase the irnpedance of the ballast as the linevoltage increases.

The invention will be further illustrated by reference to theaccompanying drawing which is a circuit ,diagram of one embodiment ofthe invention..

The arc lamp 10, which may be a high pressure arc lamp of theY compacttype, is supplied from an alternating current source through the leadsY12 and 14 and a constant inductive ballast 16. The power windings 18and 20 of a pair of saturable reactors 22 and`24 are connected inparallel with the ballast 16, and therefore with each other, to form anadditional, variable ballast. The

rectifiers 26 and 28,y each associated with one of .the

power -`windings 13 and 20, respectively, eliminateone half-wave fromthe corresponding winding. p l

In4 order .to varypthe-,impedance in the windings 18 and 20 forincreasing orv decreasing the totalballast in,

the supply circuit/the` reactor 22 is provided with two i controlwindings 30 and 32. In a similark mannen'con- Variation of the impedancein the power windings as a function of the supply voltage is obtained bymeans of i direct current signals through the control windings, wherebyeach half-wave ofthe total` supply current is separately subjected tothis correction. Since the impedancein the power windings 18 and 20 isan inverse kfunction of the degree of. magnetic saturation in the cores38 and 40, av

decrease in saturation andrtherefore an increase in impedance must beobtained from an increase` in supply` voltage. This is accomplished, inaccordance with the invention, by applying aconstant magnetic field tothe cores 38 and 40, the force of this field exceeding that required foroptimum current supply' to the lamp 10.` For this purpose, the controlwindings 30 and 34 are energized by a sufficiently strong,lconstantdirect current signal which may be obtained from any suitable .currentsource. In practice, the required current is` preferably derivedfromthesupply lines 12 and L14 over' taps 42 and 44, a voltagestabilizer 46, which may comprise a saturable reactor 48 andA a loadingcapacitor 50, and a full'- wave bridge-,type rectifier 52.

The second, weaker direct current signal, which lmust be a function ofthe supply voltage, is obtained by means of taps 54 and 56, through atransformer 58 and a secondA Patented Aug. 4, 1964- been shown as beingwound in the opposite sense. Obviously, the same effect can be obtained,eg., by reversing the polarity of one of the rectifiers.

From the foregoing it will be understood that the cores 38` and 40 aresubjected'to the action of a differential magnetic field which is theresult of the comparatively greater magnetic force generated by theconstant current signalv flowing through windings 30 and 34, diminishedb'y the opposed magnetic force at any particular instant and obtainedfrom the second pair'of control windings 32 and 36. In practice, and inorder to obtain a large operating range, it has been found advantageousto provide a current in the windings 30 and 34 about twice as strong asthe average or optimum current in the windings 32 and 36. In operation,a decrease in line voltage and therefore in the signal current throughcontrol windings 32 and 36 results in an increase of magnetization inthe The impedance then decreases to permit more current to flow throughthe power windings 18 and 20 and through the-lamp. With increasedlinevoltage, conditions are reversed, that is, with an increase in linevoltage, inagnetization in the cores decreases to increase the impedanceinthe power windings. Less current in the supply circuit flows` throughthe lamp and the desired result ofrpower stabilization is obtained. Inthis regard it will be noted that the magnetic fields set up by theconstant current signal in the windings 30 and 34 prevail over thevaryingu supply signal fields generated by the coils 32 and 36; that istrue at any particular instant. In each case, the resulting differentialmagnetic field therefore has the polarity of the first mentioned fieldand varies as an inverse -function of the supply signal through thewindings 32 and 36.

In -one particular example, the supply voltage had a nominalvalue of115- volts and actually variedA from about 100 volts to 130 volts. Theresulting variable control voltage at the secondary of the transformer58 varied from Vmm when the line voltage was 100 volts. to Vmm when theline voltage was 130 volts. The constant biasing voltage at the outputof the circuit 46 was equal to Vmax., the maximum value of the variablecontrol voltage. Now, withy the constant biasing and yvariable controlsignals Vbeingapplied in opposition to the magnetic amplifier, theycancel out when the line voltage is at the maximum value of 130 volts.Under these conditions the impedance of the magnetic amplifier is highand essentially no-` current flows through it, When the Vline `voltagedrops to 100 volts, however, the differential bias saturates themagnetic amplifier and its impedancedrops sufficiently to maintain thearc lamp voltage at a substantially constant level. The minimumimpedanceof the magnetic amplifier is thereforev several times that of the,ballast 4, and the power handling capacity of the magnetic amplifier isonly a minor factor of that of the ballast.

The subject matter of thisr application is related to that' disclosed inco-pending applicaion Serial No. 781,222, filed December 18, 1958, nowabandoned.

It will be` obvious to those skilled in the art that many modificationsmay be made within the scope ofthe present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is: v

1'. An automatically regulated ballast circuit comprising alternatingcurrent input means connectable to a current supply, a ballast connectedin series in the input means, a pair of saturable reactors having. powerwindings, the ballast including the power windings, means for directingone half-wave `of the supply current through the power windings of onereactor, means for directing the other half-wave of the supply currentthrough the power windings of the other reactor; each reactor having acore and first and second control windings; means for supplying a first,stabilized direct currentvsignal to the first control winding of eachreactor for magnetically biasing both cores equally and beyond thesaturation degree required for optimum current supply conditions; meansfor deriving, from the alternating current supply, a second directcurrent signal which is a function of the supply voltage; and means forsupplying said second signal to the second controlV winding of eachreactor for opposing, equally in each core, the saturation produced bythe first stabilizedy direct current signal in the first control windingwith the second signal.

2. An automatically regulated ballast circuit compris` ing alternatingcurrent input means connectable to a current supply, a ballast connectedin series in the input means, a Vpair `of Isaturablel reactors havingpower windings, the ballast including` the power windings, means fordirecting one half-wave of the supply current through the power windingsof one reactor; means lfor directing the other half-wave of the supplycurrent through the power 1 windings of the other reactor; each reactorhaving a core o f each reactor for opposing, equally in both cores, theAand firs-t and second control windings; means Afor supply-ysaturationproduced by the first stabilized directk current signal inthefirst control windings. I

3. An automatically regulated ballast circuit comprising alternatingcurrent input means connectable to a current supply, a ballast connectedinseries in the input means, the ballast comprising an inductance havingcom` paratively. low impedance land the power windings of a dualmagnetic amplifierof comparatively high impedance,

each winding being connectedin parallel with-said inductance; a pair ofrectiers oppositely poledrelativeto each other and each associated withone of the said pair ofv power windings, the du-al magnetic amplifierhaving i' trol windings of each core to increase the two cores, a pairof control windings being associated with each core; circuitryincludingA a stabilizer and a first bridge- Ytype full-wave rectifierfor deriving-a first, constant direct current signal from said powerIsupply means; means for applying said first signal to one of thecontrol windings of each core tol decrease the impedance in the powerwindings below the impedance level for optimum current supplyconditions; circuitry including a transformer and a second full-wavebridge-type rectifier for deriving, from the alternating currentsupply,` atsecond direct current signal which is a function of thesupplyrvoltage.; andmeans for applying said Isecond signal to the otherconthe power windings.

References Cited in -the file of this patent UNITED STATES PATENTS2,399,377 vPanna et a1. Apr. so, 1946 2,786,968 Kabak Mar. 26,v 195,72,926,287 Bird Feb. 23, 1960 impedance in

1. AN AUTOMATICALLY REGULATED BALLAST CIRCUIT COMPRISING ALTERNATINGCURRENT INPUT MEANS CONNECTABLE TO A CURRENT SUPPLY, A BALLAST CONNECTEDIN SERIES IN THE INPUT MEANS, A PAIR OF SATURABLE REACTORS HAVING POWERWINDINGS, THE BALLAST INCLUDING THE POWER WINDINGS, MEANS FOR DIRECTINGONE HALF-WAVE OF THE SUPPLY CURRENT THROUGH THE POWER WINDINGS OF ONEREACTOR, MEANS FOR DIRECTING THE OTHER HALF-WAVE OF THE SUPPLY CURRENTTHROUGH THE POWER WINDINGS OF THE OTHER REACTOR; EACH REACTOR HAVING ACORE AND FIRST AND SECOND CONTROL WINDINGS; MEANS FOR SUPPLYING A FIRST,STABILIZED DIRECT CURRENT SIGNAL TO THE FIRST CONTROL WINDING OF EACHREACTOR FOR MAGNETICALLY BIASING BOTH CORES EQUALLY AND BEYOND THESATURATION DEGREE REQUIRED FOR OPTIMUM CURRENT SUPPLY CONDITIONS; MEANSFOR DERIVING, FROM THE ALTERNATING CURRENT SUPPLY, A SECOND DIRECTCURRENT SIGNAL WHICH IS A FUNCTION OF THE SUPPLY VOLTAGE; AND MEANS FORSUPPLYING SAID SECOND SIGNAL TO THE SECOND CONTROL WINDING OF EACHREACTOR FOR OPPOSING, EQUALLY IN EACH CORE, THE SATURATION PRODUCED BYTHE FIRST STABILIZED DIRECT CURRENT SIGNAL IN THE FIRST CONTROL WINDINGWITH THE SECOND SIGNAL.